Control system for a load handling attachment on an industrial truck



April 27, 1965 E. A. HORTON CONTROL SYSTEM FOR A LOAD HANDLINGATTACHMENT ON AN INDUSTRIAL TRUCK 3 Sheets-Sheet Filed March 14, 1963INVENTOR. t". 14. HORTON ATTORNEY April 27, 1965 E. A. HORTON 3, 8 ,514

CONTROL SYSTEM FOR A LOAD HANDLING ATTACHMENT ON AN INDUSTRIAL TRUCKFiled March 14, 1965 3 Sheets-Sheet 2 16a INVENTOR.

f. 4 How To/v A nl 27, 1965 HORTON 3,180,514

CONTROL SYSTEM FOR A LOAD HANDLING ATTACHMENT ON AN INDUSTRIAL TRUCKFiled March 14, 1963 3 Sheets-Sheet 3 15 454 I I :Ilijfi I 1 LJ l 1 I 1160/ 16 INVENTOR 5 4 #0R TON r; BY

United States Patent CQNIRQL SYSTEM F023; A ELQAB HANELLYG ATTACHIl EENTON AN @IBUdTRlAL TRUCK Earl A. Horton, Philadelchia, Pa, assignor, byusesne assignments, to Yale 8; Towne, inc, New York, N.Y., a eorncany of(E hic Filed Mar. 14, 1963, Ser. No. 265,213 5 Clair-"us. (Cl. 214-652}This invention relates to industrial trucks. More particularly, theinvention relates to a control system for operating a plurality ofhydraulically actuated load manipulating devices mounted on the liftingcarriage of such a truck.

It has heretofore been proposed to control such hydraulically actuateddevices through a hydraulic directional control valve mounted on thetruck, adjacent the operators seat, and electrically operated valvesmounted on the load carriage, with the valves being operated by electricswitches mounted on the truck. This arrangement provides individualcontrol of the plurality of hydraulically actuated devices on the loadcarriage, while utilizing only one pair of hydraulic hoses and arelatively small multiple conductor electric cable leading from thetruck to the load carriage.

With an arrangement of this type, however, it is possible, particularlyif the switches are mounted on the handle for the directional controlvalve, for the operator to accidentally release a switch therebystopping operation of one hydraulic device and immediately startoperation of a second hydraulic device. This can be dangerous. Thus, theoperator may release a switch to stop operation of a hydraulic device onthe load carriage for rotating a load, and by doing so, simultaneouslystart operation of a load clamping device, with resulting crushin ordrop ping of a load.

This invention provides an improved arrangement of this type in whicheither actuating or releasing a switch is ineffective to operate theelectric valve on the load carriage, unless the directional controlvalve is in a neutral position in which no fluid is supplied to thehydraulic devices. Thus, with this arrangement, it is impossible to stopoperation of one hydraulic device and simultaneously start operation ofa second hydraulic device.

The invention and its advantages having been described, a more detaileddescription of two forms of the invention is given hereafter byreference to the accompanying drawings w erein:

FIG. 1 is a side elevational view of a lift truck of the type on whichthe control system of the invention may be advantageously used;

FIG. 2 is a top plan view of the truck shown in FIG. 1;

FIG. 3 is a combined electrical and hydraulic diagram showing one formof control system constructed in accordance with the invention forcontrolling operation of three hydraulically operated load manipulatingdevices mounted on the lifting carriage of the truck shown in FIGS. 1and 2; and

FIG. 4 is a combined electrical and hydraulic diagram showing a secondcontrol system constructed in accordance with the invention forcontrolling operation of three hydraulically operated manipulatingdevices mounted on the lifting carriage of the truck shown in F168. 1and 2.

Referring to the drawings and in particular to FIGS. 1 and 2, there isshown an industrial truck T of the type on which the control system ofthe invention may be used advantageously.

The truck '1 is of conventional construction and includes uprights illand a lifting load carriage 11 which is mounted for vertical movement onthe uprights ll Three conventional hydraulically actuated load maniput"dtldfil s: cc Patented. 2?, 1%55 lating devices are shown mounted on thelifting carriage T e first device is a load clamping device, generallyindicated at 312, and includes a pair of clamping arms 13 and 1'4 and apair of hydraulic rams 1d and 16 for moving the clamping arms toward andaway from each other to clamp or release a load.

The second device is a rotating device, generally indicated at 17, andincludes a hydraulic ram or motor 18 by which the clamping device 12 maybe rotated about a horizontal axis relatively to the load carriage 11.

The third device is a side shifting device, generally indicated at id,and includes a hydraulic ram 26 by which the clamping device 12 androtating device 17 may be shifted as a unit in a direction transverselyof the load carriage ll. Each of these hydraulic devices are ofconventional, well-known constructions, and the details thereof for 3.no part of the invention.

Fluid for operating the rams i5, i6, 18 and 2% is supplied from a singlepair of hoses 21 and 22, extending between the load carriage ll and afluid pump, or other pressure source, mounted on the truck. Thedirection of flow of tluid through the hoses is controlled through areversing valve 23 mounted on the truck body, which is actuated throughmovement of a handle 24. As will be described in detail, fluid from thehoses 21 and 22 is selectively directed to rams 15' and 16 or to ram 1%or ram through electrics-ll actuated valves mounted on the load carriageand operated by switches which are mounted on the truck body andconnected to the valves by a multiple conductor electric cable 25. Bythis arrangement, individual control of the three hydraulically actuateddevices l2, l7 and 1% is obtained, while utilizing only a single pair ofhoses and a relatively small multiple conductor electric cable leadingfrom the truck to the load carriage.

Referring now to PEG. 3, there is shown diagrammatically, one form ofcontrol system constructed in accordance with the invention forcontrolling operation of the rams of the three devices 12, 1'7 and 19.In the system illustrated in El 3, two solenoid operated valves 26 and2?, which are mounted on the carriage H, are used to selectively controlthe flow of fiuid from the pair of hoses 2.1 and 22 to the rams 15, l6,l3 and 20. As will be described in detail hereafter, these two valvesare actuated by push buttons and 29, which are conveniently moun ed onthe handle 24 of the reversing valve 23.

in FIG. 3, each of the solenoid operated valves 26 and 27 are shown inthe non-actuated position and the various relays are shown in thenon-energized condition. Reversing valve 23 is shown in a neutralposition in which the hoses 21 and 22 are disconnected from the pump36), or other source of fluid pressure.

Assuming that the operator wishes to clamp 21 load, he moves the hande24 in the direction of the arrow A, without operating push buttons 23and 2d. This moves the reversing valve 23 to a position in which thehose 21 is connected with a pressure line 31 from a fluid pressuresource Eli), while hose 2?. is connected with a return line 32 to thepressure source 39. Fluid under pressure flows from the fluid pressuresource through the hose 21, through solenoid operated valve 26, andthrough solenoid operated valve 27 to the left-hand side of the ram 15,causing the piston a thereof to move to the right.

The ram 15 is connected in parallel with the ram by a conduit 33, sothat fluid from the hose 21 also flows to the right-hand side of the ramto, causing the piston lea thereof to move to the left. As the piston15a moves to the right and the piston lea moves to the left, fluid onthe right-hand side of piston 15:: and the fluid on the leit-hand sideof piston lea flows through a conduit 33a, which connects the oppositeends of the rams in parallel,

3. through the solenoid operated valve 27, the solenoid operated valve26, the hose 22, the reversing valve 23 and the return line 32 back tothe pressure source 39.

The clamping arms 13 and 14 are thus moved toward each other by the rams15 and 16 to clamp the load. When the load is properly gripped by theclamping arms 13 and 14, the operator moves the handle 24 back to theneutral-position, thereby disconnecting the hoses 21 and 22 from thepressure source 3% and trapping. the fluid in the rams 15 and-16 so thatthe load is held clamped between the clamping arms 13 and 14. 7

As the handle 24 is moved in the direction of the arrow A, to actuatethe rams 15 and 16, electrical contacts 3 which are held open by a cam24a on the handle 24 when the handle 24 is in the neutral position,close, and contacts 35, which are held closed by the cam 24:: of thehandle 24 in the neutral position of the handle open. The opening ofcontacts 35' prevents a circuit from being completed to the solenoid 26aof the solenoid operated valve 26 and also to the solenoid 27a of thesolenoid operated valve 27, so that if either push button 28 or pushbutton 29 is accidentally pressed while the valve 23 is shifted tooperate the rams 15 and 16, the pressing of the buttons 28 and 29 isineffective to operate the rams 18 and 20. Thus once the operator hasmoved the handle 24 from the neutral position to operate the rams 15 and16, he cannot accidentally start operation of the ram 18 or 20, withoutfirstreturning the handle 24 to neutral position.

To unclamp the load, the handle 24 is moved in the direction of thearrow Bf The system then functions in the same manner as in clamping theload except that the direction of the flow of fluid is reversed so thatthe clamps V energize the solenoid 26a of the solenoid operated valve 726 to shift the valve 26 and to energize a relay 39 cansing normallyclosed contacts 39a thereof to open and causing normally open contacts3% thereof to close.

The'shifting of valve 26 by energizing the solenoid 26a connects hose 21to the lower end of ram 13' and connects hose 22 to the upper end of ram18, so that when the reversing valve 23 is shifted to the left bymovement of the handle 24 in the direction of the arrow A, fluid underpressure is applied to the ram 18 to extend the piston and rotate theload. At the same time, fluid is held trapped in the rams 15 and 16 sothat the load remains clamped. As the handle 24 is moved from theneutral position, contacts 34 close and contacts open.

Closing of contacts 34' forms a holding circuit through closed contacts3% around the contacts 28a, so that once the button 28 is pressed andthe handle 24 is moved from the neutral position, accidental releasingof the push button 28 to open contacts 28a is ineffective to de-energizethe solenoid 2% of the solenoid operated valve 26. Thus, once the pushbutton 28 has been pushed and the handle 24 moved from the neutralposition, solenoid 26a cannot bode-energized with resulting simultaneousoperation of the clamping rams 15 and 16, except by first moving thehandle 24 back to the neutral position.

- The opening of contacts 39a of the relay 39 opens the circuit throughcontacts 39a of push button 29 so that accidental closing of push button22 is ineffective at this time to energize the solenoid 27a of thesolenoid operated valve 27 to operate the ram 219.

Assuming that the load has been rotated to the desired position byoperation of the ram 18, the operator moves the handle 24 back to theneutral position thereby discona i I necting the hoses 2,1 and 22 fromthe fluid pressure source 30. As the handle 24 is moved back to theneutral position, contacts 34 are again opened and contacts 35 areclosed. As the contacts 34 are again opened, the holding circuit throughthe closed contacts 3% is broken so that the relay 39 and the solenoid25a of the solenoid operated valve 26 are de-energized and valve 26moves back to the initial position, as shown in the drawing, trappingthe fluid in the ram 18 to hold the load in'the rotated position.

To rotate the load in the opposite direction, push button 2% is pressedand the handle 24' moved in the direction of the arrow B. The systemthen functions in the same manner as just described with the flow offluid to the ram 18 being reversed to reverse the direction of rotationof v the load.

Assuming now that the operator wishes to side shift the load, he pressespush button 29 and moves the handle 24 in the direction of the arrow Ato shift the valve 23 to the right.

Pressing push button 29 closes contacts 29a to complete a circuitthrough closed contacts 35, closed contacts 39a of the relay 39 and thebattery 36 to energize the solenoid 27a of the solenoid operated valve27 to'shift the valve 27 and to energize relay 38 to open contacts 38athereof and close contacts 38b.

The shifting of the valve 27 connects the hoses 21 and 22 to the ram 29,sothat when the handle 24 is moved in. the direction of the arrow A,fluid is applied to the ram 20 to shift the load. As the handle 24 ismoved from the neutral position, contacts 34 again close and contacts35' open. Closing of contacts 34 completes a holding circuit through theclosed contactsisdb, around contacts 29a, to hold the relay 38 and thesolenoid 27a of the solenoid operated valve 27 energized should the pushbutton 29' accidentally be released. Thus, the solenoid 27a cannot bede-energized to shift the valve 27 except by movement r of the handle 24back to the neutral position.

At the same time, the opening of contacts 38a by energizing relay 3%opens'the circuit through contacts 23a so that the accidental pressingof push button 28 is ineffective to energize the solenoid 2% of thesolenoid operated valve 26, once the push button 29 has been pushed andthe handle 24 moved from the neutral position.

Side shifting of the load is stopped by again returning the handle 24 toneutral position to' disconnect the hoses '21 and 22 from the pressuresource 30 and to close contacts35 and open contacts 34. Opening ofcontacts 34 breaks the holding circuit through closed contacts 33b sothat the relay 38 and the solenoid 27a are de-energized and valve 27moves back to the original position, trapping the fluid in the ram 20.

To side shift the load in the opposite direction, the push button 29 ispressed and the handle 24 moved in the direction of the arrow B toreverse the. flow of fluid to th ram 20. V a

Thus, it can be seen that by this arrangement shown in FIG. 3, eitheractuating or releasing one of the push buttons 28 or 29 is ineifectiveto operate the solenoid operated valves 26 and 27, unless the handle 24and therefore the reversing valve 23 are in the neutral position, inwhich no fluid is supplied to the hydraulic rams 15, 16, 18 and 20.Thus, with this arrangement, it is impossible to stop operation of onehydraulic device and simultaneously start operation of a secondhydraulic device.

Referring now to FIG. 4,'there is shown aslightly dif ferent controlarrangement which may be used when solenoid operated valves of the typeshown in FIG. 3 are not available for the particular volumetricrequirements of the system. In this arrangement, two solenoid operatedvalves are used for controlling the fluid to each hydraulic device.Thus, two valves 41 and 42 are used for controlling the flow of fluid tothe rams 15 and 16 of the clamping device, two valves 43 and 44 are usedfor controlling the flow of fiuidto the ram 18 ofthe rotating device andtwo valves .5 and 46 are used for controlling the flow of fluid to theram Zll of the side shifting evice. Each of these solenoid operatedvalves is identical, and, when non-energized, as shown in PEG. 4,prevent return flow of fluid from each side of the rams while allowingfluid to be applied to each side of the rams. When energized, the valvesallow fluid to flow in both directions from the ram.

Three push buttons 47, E3 and 49, conveniently mounted on the handle 24,are used to control the operation of the solenoid operated valves of thehydraulic devices.

Assuming that the operator wishes to clamp a load, he first presses pushbutton 47 and moves the handle 24 in the direction of the arrow A.Pressing push button 47 closes contacts 470 completing a circuit fromthe battery 36 through closed contacts 35, closed contacts Sea of arelay 53 and closed contacts 54:: of a relay 54 to energize solenoids41a and 42a of the valves ll and 412, and also to energize a relay 5'5.

Energizing solenoids 41a and 22a shifts the valves to a position inwhich fluid may flow to the rams and 1%, so that shifting the reversingvalve 23 to the left by movement of the handle 24 in the direction ofthe arrow A, applies fluid pressure through hose 21 to the left-handside of the ram 15 and also to the right-hand side of ram 16 to move thepiston 15a to the right and piston 16a to the left. As the piston 15::moves to the right and the piston 16a moves to the left, the fluid onthe opposite sides of the pistons flows through the valve 42; to thereturn hose 22. The clamping arms 13 and 1d are thereby moved togetherto clamp the load.

Energizing relay 55 causes normally open contacts 55a to close andnormally closed contacts 55!: and 556 to open. Closing contacts 55aforms a holding circuit through contacts 34, which close as the handle24 is moved in the direction of the arrow A, around the contacts 47a, sothat once the button 47 is pressed and the handle 24 moved from theneutral position, accidental releasing of the button 47 to open thecontacts 470 is ineifective to tie-energize the solenoids 41a and 42a ofthe solenoid operated valves ll and 42. The opening of contacts 551) and55s breaks the circuits through contacts 48a and 49:: so that accidentalpressing of push buttons 43 and 49 is ineffective at this time toenergize the solenoids of the valves 43, 44, 45 and 4-5 to operate therams 18 and 2% When the load has been properly clamped, the operatormoves the handle 24 back to neutral position thereby disconnecting thehoses 21 and 22 from the fluid pressure source 38. As the handle 24 ismoved back to neutral position, contacts 34 are again opened andcontacts 35 are closed. As the contacts are again opened, the holdingcircuit through the closed contacts 55:: is broken so that relay 55 andthe solenoids 41a and 42a of the valves 41 and 42 are de-energized andthe valves 41 and 42 moved back to the initial position shown in thedrawing, trapping the fluid in the rams 15 and in to hold the loadclamped.

To unclarnp the load, the operator again presses push button 47 andmoves handle 24 in the direction of the arrow B. The system thenfunctions in the same manner as just described with the flow of fluid tothe rams 15 and 15 being reversed to move the clamping arms away fromeach other.

Assuming that the load has been properly clamped and the handle 24returned to neutral position, the operator may operate ram 18 to rotatethe clamped load by pressing button 48 and then again moving the handle24- in the direction of the arrow A.

Pressing push button 43 closes contacts 48:: completing a circuit fromthe battery 3-? through closed contacts 35 and closed contacts 551) and54b of relays 55 and S l to energize solenoids 43a and 44a of thesolenoid operated valves 43 and 44- to shift the valves 43 and 44. Theclosing of the contacts 43a also completes a circuit to energize therelay 53 to open contacts 530 thereof and to close contacts 531) and530.

,lsasis The shifting of the valves 43 and 44 connects hose 2f to theupper end of the ram 13 and connects hose 22 to the lower end of ram 18,so that when the reversing valve 23 is shifted to the left by movementof the handle 24 in the direction of the arrow A, fluid under pressureis applied to the ram 13 to extend the piston 13a thereof to rotate theload. I

The closing of contacts 53b forms a holding circuit through closedcontacts 34 around the contacts 43a, so that once the button 4% ispressed and the handle 24 is moved from the neutral position, accidentalreleasing of the push button 48 to open contacts 48a is ineffective torte-energize the solenoids 43a and 44a of the solenoid operated valves43 and 44.

The opening of contacts 53a and 530 breaks the circuit through contacts47!: and 49a so that accidental pressing of buttons 47 and 49 isineffective to energize the solenoids of the solenoid operated valves41, 42, 45 and as.

When the load has been rotated to the desired position by operation ofthe ram 18, the operator moves the handle 24 back to the neutralposition, thereby disconnesting the hoses Z1 and 22 from the fluidpressure source 3%). As the handle 24 is moved back to neutral position,contacts 34 are again opened and contacts 35 are closed. As the contacts34 are again opened, the holding circuit through the closed contacts531) is broken so that the relay S3 and the solenoids 43a and 44:: arede-energized and valves 43 and 44 moved back to the initial position,shown in the drawing, trapping the fluid in the ram 18 to hold the loadin the rotated position.

To rotate the load in the opposite direction, push button 48 is againpressed and the handle 24 moved in the direction of the arrow B. Thesystem then functions in the same manner as just described with the flowof fluid to the ram 18 being reversed to reverse the direction ofrotation of the load.

Assuming now that the operator wishes to side shift the load, he pressespush button 49 and moves the handle 24 in the direction of the arrow Ato shift the valve 23 to the left.

Pressing push button 4% closes contacts 4% to complete a circuit fromthe battery 36 through the closed contacts 35 and closed contacts 53cand 550 to energize the relay S4 and to energize the solenoids 45a andida of the solenoid operated valves 35 and 4K to shift these valves.

The shifting of the valves 4-5 and 46 connects the hose 21 to theleft-hand end of the ram 20 and connects the hose 22 to the right-handend of the ram 29, so that when the handle 24 is moved in the directionof the arrow A, fluid is applied to the ram 26 to shift the load. Theclosing of contacts 540 when the relay 54- is energized completes aholding circuit through contacts 34, around the contacts 49a, so thatonce the button 49 is pressed and the handle 24 moved from the neutralposition, accidental releasing of the button 49 is inelfective tode-energize the solenoids 45a and 46a of the valves 45 and 46.

The opening of contacts 54a and 54b breaks the circuits through contacts48a and 47a so that accidental pressing of push button 47 or 49 isinetfective at this time to energize the solenoids of the valves ll, 42,43 and 44 to operate the rams 15, 16 and 18. The side shifting of theload is stopped by again returning the handle 24 to neutral position todisconnect the hoses 21 and 22 from the pressure source 39 and to closecontacts 35 and open contacts 34. The opening of contacts 34 breaks theholding circuit through contacts 540 so that the relay 54 and thesolenoids 45a and 46a are de-energized and the valves 4-5 and 46 movedback to the original position, trapping the fluid in the ram 20.

To side shift the load in the opposite direction, the push button 49 ispressed and the handle 24 is moved in the direction of the arrow B toreverse the flow of fluid to the ram 29.

Thus, it can be seen by the arrangement shown in FIG. 4, that eitheractuating or releasing the push buttons 47, 48 and 49 is ineffective tooperate the solenoid operated valves 41, 42, 43, 45 and 46, unless thehandle 24 and therefore the reversing valve 23 are in the neutralposition in which no fluid is supplied to the hydraulic rams. Thus withthis arrangement, it is impossible to start operation of one hydraulicdevice and simultaneously start operation of a second hydraulic device.7

From the preceding description, it can be seen that there is provided anovel arrangement in which either actuating or releasing a switch isineffective to operate the electric valve on the load carriage, unlessthe directional control valve is in a neutral position in which no fluidis supplied to the hydraulic device. Thus accidental stopping of oneoperation and simultaneous starting of a second operation resulting inthe creation of a dangerous situation is effectively prevented.

While two embodiments of the invention have been shown and described, itwill be appreciated that this is for the purpose of illustration andthat changes'and modifications may be made therein without departingfrom the spirit and scope of the invention.

I now claim:

' 1. In an industrial truck having a main frame, a lifting carriagemounted for movement on said mainframe, a

' plurality of hydraulically actuated load manipulating devices on saidcarriage, a source of fluid pressure on said main frame, flexibleconduit means extending between said main frame and said liftingcarriage, a hydraulic control valve on said main frame movable between aneutral position in which said flexible conduit means is disconnectedfrom said source of fluid pressure and a power position inwhich saidflexible conduit means is connected to said source of fluid pressure,power operated hydraulic valve means on said carriage operable toselectively direct fluid from said conduit means to one of saidhydraulically actuated load manipulating devices, control means on saidtruck for selectively operating said power operated valve means, andmeans interconnecting said hydraulic control valve and said poweroperated valve means for preventing operation of said power operatedvalve means when said hydraulic control valve is in said power positionwhile permitting operation of said power operated valve means when'saidhydraulic control valve is in neutral. position whereby simultaneousstopping of the operation of one hydraulic device and starting operationof a second hydraulic device is prevented.

2. In an industrial truck having a main frame, a lifting carriagemounted for movement on said main frame, a plurality of hydraulicallyactuated load manipulating devices on said carriage, a source of fluidpressure on said main frame, flexible conduit means extending betweensaid main frame and said lifting carriage, a hydraulic control valve onsaid main frame movable between a neutral position in which saidflexible conduit means are disconnected from said source of fluidpressure and a power position in which said flexible conduit means areconnected'to said source of fluid pressure, electrically operatedhydraulic valve means on said carriage operable to selectively directfluid from said conduit means to one plurality of hydraulically actuatedload manipulating devices on said carriage, a source of fluid pressureon said main frame, flexible conduit means extending between said mainframe and said lifting carriage, a hydraulic.

control valve on said main frame including handle means for moving saidvalve between a neutral position in which said flexible conduit means isdisconnected from said source of fluid pressure and a power position inwhich said flexible conduit means is connected to said source of fluidpressure, electrically operated hydraulic valve means on said carriageoperable to selectively direct fluid from said conduit means to one ofsaid hydraulically actuated load manipulating devices, switch means onsaid handle electrically operated valve means when said hydrauliccontrol valve is in said power position while permitting operation ofsaid electrically, operated valve means by said switch means when saidhydraulic control valve is in neutral position whereby stoppingoperation of one hydraulic device and simultaneous starting operation ofa second hydraulic device is prevented.

4. In an industrial truck having a main frame, a lifting carriagemounted for movement on said main frame, a plurality of hydraulicallyactuated load manipulating devices on said carriage, a source of fluidpressure on said main frame, flexible conduit means extending betweensaid main frame and said lifting carriage, a hydraulic control valve onsaid main frame movable between a neutral position in which saidflexible conduit means are of said hydraulically actuated loadmanipulating devices, I

switch means on said truck for selectively operating said electricallyoperated valve'means, and means interconnecting said hydraulic controlvalve and said electrically operated valve means for preventingoperation of said electrically operated valve means when said hydrauliccontrol valve is in said power position while permitting operation ofsaid electrically operated valve means when said hydraulic control valveis in neutral position whereby simultaneous stopping of the operation ofone hydraulic device and starting operation of a second hydraulic deviceis prevented. 1 I

3. In an industrial truck having a main frame, a lifting carriagemounted for movement on said main frame, a

disconnected from said source of fluid pressure and a power position inwhich said flexible conduit means are connected to said source of fluidpressure, electrically operated hydraulic valve means on said carriagefor each hydraulically operated device for connecting the hydraulicdevices with said conduit means, switch means on said truck forselectively operating the electrically operated hydraulic valve means ofeach hydraulically operated device, and means interconnecting saidhydraulic con- 5. In an industrialtruck having a main frame, a lift ingcarriage mounted for movement on said main frame, at least twohydraulically actuated load manipulating devices on said carriage, asource of fluid pressure on said main frame, flexible conduit meansextending between said main frame and said lifting carriage, a hydrauliccontrol valve on said main frame movable between a neutral position inwhich said flexible conduit means is disconnected from said source offluid pressure and a power position in which said flexible conduit meansis connected to said source of fluid pressure, electrically operatedhydraulic selector valve means on said carriage operable to selectivelydirect fluid from the said conduit means to either one of saidhydraulically actuated load manipulating devices, switch means on saidtruck for operating said electrically operated selector valve means, andmeans interconnecting said hydraulic control valve and said electricallyoperated selector valve means for rendering said switch meansineffective to change the position of said selector valve means whensaid hydraulic control valve is in power position while permittingchanging of the position of said selector valve means by said switchmeans when said'hydraulic control valve is in neutral position wherebystopping operation of one hydraulic device and simultaneous startingoperation of a second hydraulic device is prevented.

References Cite by the Examiner UNITED STATES PATENTS Harsch 60-52 Tyler121-41 Balch 200-157 Schroeder 214-652 Randall 121-40 Schenkelberger219-653 Quayle 60-97 Troche 60-97 MacMillin 60-97 Bullard 200-157 X 10HUGO O. SCHULZ, Primary Examiner.

MORRIS TEMIN, Examiner.

1. IN AN INDUSTRIAL TRUCK HAVING A MAIN FRAME, A LIFTINBG CARRIAGEMOUNTED FOR MOVEMENT ON SAID MAIN FRAME, A PLURALITYH OF HYDRAULICALLYACTUATED LOAD MANIPULATING DEVICES ON SAID CARRIAGE, A SOURCE OF FLUIDPRESSURE ON SAID MAIN FRAME, FLEXIBLE CONDUIT MEANS EXTENDING BETWEENSAID MAIN FRAME AMD SAID LIFTING CARRIAGE, A HYDRAULIC CONTROL VALVE ONSAID MAIN FRAME MOVABLE BETWEEN A NEUTRAL POSITION IN WHICH SAIDFLEXIBLE CONDUIT MEANS IS DISCONNECTED FROM SAID SOURCE OF FLUIDPRESSURE AND A POWER POSITION IN WHICH SAID FLEXIBLE CONDUIT MEANS ISCONNECTED TO SAID SOURCE OF FLUID PRESSURE, POWER OPERATED HYDRAULICVALVE MEANS ON SAID CARRIAGE OPERABLE TO SELECTIVELY DIRECT FLUID FROMSAID CONDUIT MEANS TO ONE OF SAID HYDRAULICALLY ACTUATED LOADMANIPULATING DEVICES, CONTROL MEANS ON SAID TRUCK FOR SELECTIVELYOPERATING SAID POWER OPERATED VALVE MEANS, AND MEANS INTERCONNECTINGSAID HYDRAULIC CONTROL VALVE AND SAID POWER OPERATED VALVE MEANS FORPREVENTING OPERATION OF SAID POWER OPERATED VALVE MEANS WHEN SAIDHYDRAULIC CONTROL VALVE IS IN SAID POWER POSITION WHILE PERMITTINGOPERATION OF SAID POWER OPERATED VALVE MEANS WHEN SAID HYDRAULICCONTROLS VALVE IS